Significant progress has been made in vehicular braking systems in recent years. Among these developments are anti-lock braking systems (ABS) and regenerative braking systems. The latter is used in electric and hybrid-electric vehicles. In regenerative braking systems, a vehicle's brake pedal is mechanically decoupled from downstream braking circuits. A sensor associated with an input rod coupled to a brake pedal provides an electrical signal to an electronic control unit (ECU). The signal is representative of the brake pedal position. Since the brake pedal is mechanically decoupled from the downstream braking circuits, a brake pedal feel simulator is often used to simulate the feel of a conventional braking system by providing a force feedback to the vehicle operator at the brake pedal. At the same time, the ECU controls the braking system to apply a braking force consistent with the brake pedal position. An electrical regenerative system and/or a hydraulic braking system provide the necessary braking force.
In the event of a failure of the hydraulic system and/or the electrical regenerative system, it is necessary for the braking system to switch modes of operation so that the brake pedal is mechanically coupled to the downstream brake circuits. In such a failure mode, the force applied to the brake pedal is transferred to the downstream brake circuits to generate the necessary braking force to halt a vehicle.
There is a need to provide an improved braking system that is operable in a normal mode in which a brake pedal is mechanically decoupled from the downstream braking circuits and a fallback mode in which the brake pedal is mechanically coupled to the downstream braking circuits.